30 
NATJTILOIDEA. 
1852. Orthoceras suhundulatum, M‘Coy, Britisli Pal. Foss. p. 317. 
1854. Orthoceras subundulatum, Salter, in Murchison’s ‘ Siluria/ p. 231, 
Foss. Gr. 44. f. 3. 
? 1863. Orthoceras subundulatum, Has well, ^ Silurian Formation of the 
Pentland Hills,’ pi. i. if. 10, 14. 
1882. Orthoceras subundulatum, Blake, British Foss. Ceph. pt. i. 
p. 133, pi. xi. tF. 8-10. 
Char. Section circular. Bate of increase 1 in 12. Septa 
from f to ^ the diameter ; direct. Body-chamber known only by 
incomplete fragments. Siphuncle subceutral. Surface ornaments 
consisting of upward imbrications having an undulating course ; 
from 3 to 4 of them occupy the space of 1 line. 
Bemarlcs. This species is very widely distributed in Britain both 
in time and in space, if the forms recorded from various localities 
and formations be correctly ascribed to it. 
Horizon. Wenlock Shales ; Upper Ludlow. 
Localities. Nantglyn, Denbighshire ; Ludlow, Shropshire. 
Eepresented by one example. 
Orthoceras fretum ?, Blake. 
1882. Orthoceras fretum, Blake, British Foss. Ceph. pt. i. p. 135, 
pi. xiv. if. 7, la, 7b. 
Sp. Char. Section nearly circular. Bate of increase 1 in 10. 
Body-chamber short, its length is about 1 J times its basal diameter, 
with a constriction below the aperture. Septa distant less than I 
the diameter, with a convexity of more than -i- ; they are slightly 
oblique. Siphuncle eccentric, situated f across the longer diameter. 
Surface of test with very close upward imbrications, 20 in the space 
of 1 line. 
Bemarlcs. A fragment which does not show the body-chamber 
is referred to this species with considerable doubt. 
The septa are closer than in 0. Marloense, agreeing in this 
respect with 0. fretum ; the rate of tapering of the present form is 
also in accordance with the latter species. The surface markings 
are not preserved. 
Horizon. Upper Ludlow. 
Locality. Ludlow, Shropshire. 
Orthoceras Mocktreense, Sowerby. 
1839. Orthoceras Mocktreensis, Sowerby, in Murchison’s ‘ Silurian 
System,’ p. 616, pi. 6. f. 11. 
